Data from: Many paths to a common destination: morphological differentiation of a functionally convergent visual signal

Understanding the interacting outcomes of selection and historical contingency in shaping adaptive evolution remains a challenge in evolutionary biology. While selection can produce convergent outcomes when species occupy similar environments, the unique history of each species can also influence evolutionary trajectories and result in different phenotypic end points. The question is to what extent historical contingency places species on different adaptive pathways and, in turn, the extent to which we can predict evolutionary outcomes. Among lizards there are several distantly related genera that have independently evolved an elaborate extendible dewlap for territorial communication. We conducted a detailed morphological study and employed new phylogenetic comparative methods to investigate the evolution of the underlying hyoid that powers the extension of the dewlap. This analysis showed that there appear to have been multiple phenotypic pathways for evolving a functionally convergent dewlap. The biomechanical complexity that underlies this morphological structure implies that adaptation should have been constrained to a narrow phenotypic pathway. However, multiple adaptive solutions have been possible in apparent response to a common selection pressure. Thus, the phenotypic outcome that subsequently evolved in different genera seems to have been contingent on the history of the group in question. This blurs the distinction between convergent and historically contingent adaptation and suggests that adaptive phenotypic diversity can evolve without the need for divergent natural selection.解析自然选择与历史偶然性（historical contingency）共同塑造适应性演化的交互效应，仍是进化生物学领域的核心挑战之一。当物种栖息于相似环境时，自然选择可催生趋同演化结果，但各物种独有的演化历史同样会塑造演化轨迹，最终产生不同的表型终态。核心问题在于：历史偶然性在多大程度上会将物种引向不同的适应性演化路径？反过来，我们又能在多大程度上预测演化结果？ 在蜥蜴类群中，多个远缘属独立演化出了结构复杂、可伸展的喉扇（dewlap）用于领地通讯。我们开展了详细的形态学研究，并采用新型系统发育比较方法（phylogenetic comparative methods），对驱动喉扇伸展的舌骨（hyoid）演化进行了探究。分析结果显示，演化出功能趋同的喉扇似乎存在多条表型路径。 该形态结构所依托的生物力学复杂性，本应意味着适应性演化会被局限于狭窄的表型路径之中。然而，面对共同的选择压力，却演化出了多种可行的适应性方案。因此，不同属类后续演化出的表型结果，似乎取决于该类群自身的演化历史。 这模糊了趋同适应与受历史偶然性影响的适应性演化之间的界限，同时表明适应性表型多样性的演化，无需依赖趋异自然选择（divergent natural selection）即可实现。